A sash could be arranged to move vertically within a window on a pair of laterally biased guides pressed into engagement with grooves on opposite stile edges of the sash. Such guides could be mounted on the jambs to be spread apart, against their spring bias, for moving out of the sash grooves and allowing the sash to tilt and be removed from the window. A counterbalance system for such a guided sash could advantageously be arranged within the guides, but any such counterbalance system would have to accommodate the lateral movement required of the guides when the sash is tilted out of the window plane.
We have addressed the problem of a counterbalance system having components disposed within such laterally biased guides in a way that allows the guides to move apart for tilting the sash while the counterbalance system remains connected to the sash. Our counterbalance system includes several alternatives devised to accomplish this, and to do so economically and efficiently, so that the overall cost is reasonable, considering the performance of the window.
A window benefitting from our counterbalance system cooperating with such laterally biased guides can dispose a sash to run clear of the window jambs, on the relatively smaller surfaces of the guides alone. This can provide adequate frictional resistance to vertical movement of the sash, while using a relatively small lateral bias force. Such sash guides can also provide weather seals between the sash and the jamb and can hold the sash securely enough to provide adequate blowout resistance. Prototype experience has shown that such a window can operate very well, compared with existing alternatives, and can also offer desirable new design alternatives.